Tile Adhesive not set

[nearthemark]

I'm re-doing our bathroom and last week started tiling - which looked lovely except one tile was upside down and needed removing as the pattern didn't quite match. I was expecting it to be hard to get off, but actually it was incredibly easy - alarmingly so. Thankfully this highlighted a problem before I had got too far.

The history is that having removed the old tiles, the tiles behind those were incredible strong so I had PVA'd the surface before re-tiling. I know that there's two schools of thought regarding PVA, but it was the advice I was given.

The new adhesive was waterproof ready mix from a trade supplier, designed for bathrooms. When I removed the tile today, the new adhesive behind had turned to something like shortcrust pastry, not at all hard. The tiles were quite big (600x200mm). I'm not sure if I'd used too much, and have since read that with larger tiles the ready mix adhesive is not at all suitable as it does not dry. Maybe if I'd left it longer it would have done but after a week it was only the edge couple of mm that was not like pastry!

I've taken all of those tiles off, removed the old adhesive, and this time primed with BAL and bought some dry mix adhesive (Mapei Keraquick Rapid-Set Flexible Tile Adhesive).

So - will the better adhesive solve the problem? Also, can I re-use the tiles that I removed today? They have a thin layer of the ready mix adhesive which is hopefully drying! If I can still use them, would the back need priming now?

Thanks,


Mark

 

[flameport]

Ready mix adhesives can only set by the water in them evaporating - in this case that can only happen via the grout lines, and will take weeks if not months.
That is why they don't set in the tub they are sold in - it's airtight and the water cannot escape.

PVA is never used for tiling or 99% of the other uses people seem to invent for it.
Primers are only required if the background is excessively porous or dusty - and in most cases, that means it's the wrong thing to be tiling over and a primer is being used in an attempt to cover up that fact.

Cement based (supplied as a powder) adhesive will fix the tiles, as that sets by chemical reaction, not by water evaporating.
The existing tiles may be usable, but the old adhesive on them must be removed. If it doesn't scrape off, soak them in water for a few hours and then you will see how 'waterproof' the ready mix slop really is.

Mapei Keraquick Rapid-Set Flexible Tile Adhesive

If you haven't used that or similar before, beware - after mixing it is only good for about 15 minutes. Anything left in the mixing tub after that time will have to be thrown away, along with the tub.

 

[Keithmac]

I recently tiled my kittchen floor, 300mm×300mm and the adhesive had set overnight (hand mixed).

PVA if it gets wet turns slimy, so your tiles are basically sat on a slimy layer not bonded to the wall..

If I was going to tile over tile I would score the tiles first to get a good bond/ key. Personally I'd take them all off and start from scratch.

If you've not personally laid the first set it can be quite interesting to see what's underneath them and other peoples interpretation of a good job..

 

[curium]

If you've not personally laid the first set it can be quite interesting to see what's underneath them and other peoples interpretation of a good job..

Indeed!

When I took my wall tiles off to retile I found dot-and-dabbed plasterboard on top of tiles on top of plasterboard screwed to metal studwork.

 

[nearthemark]

Thanks for the comments. Rapid set was great to work with.

I'm thinking about using what's left of the bal primer to go over where previously pva'd, as the PVA was so dilute (1:5 as per instructions) some neat primer should help?


M

 

[B17NNS]

I know that there's two schools of thought regarding PVA, but it was the advice I was given.

There are two schools of thought yes. The right one and the wrong one. PVA has no place in tiling. There's science behind the reason.

 

[Keithmac]

Thanks for the comments. Rapid set was great to work with.

I'm thinking about using what's left of the bal primer to go over where previously pva'd, as the PVA was so dilute (1:5 as per instructions) some neat primer should help?


M

Try and get as much as you can off with a stainless scouring pad?.

 

[nearthemark]

Try and get as much as you can off with a stainless scouring pad?.

Thank you. Have done, used course sandpaper.

 

[opps]

Primers are only required if the background is excessively porous or dusty - and in most cases, that means it's the wrong thing to be tiling over and a primer is being used in an attempt to cover up that fact.

?

Most surfaces that you tile over are porous, unless you are tiling over tiles.

I use SBR when tiling over plaster, render, cement fibre board, etc.

Cement based (supplied as a powder) adhesive will fix the tiles, as that sets by chemical reaction, not by water evaporating.

True but the water content is critical to the hydration reaction. If the water in contact with the wall is sucked away immediately the adhesive closest to the wall will be weakened. Worst case scenario, the tiles fall off but at least the adhesive stuck to them.

 

[nearthemark]

After spending ages getting hole exactly right in tile for extractor fan, damn thing cracked when I put the screws in!!!!!

Not noticeable, but I know it's there, grrr..

 

[Keithmac]

I was expecting the worst when tiling around the socket boxes in the kitchen but got away with it, more luck than judgement..

 

[opps]

If you haven't used that or similar before, beware - after mixing it is only good for about 15 minutes. Anything left in the mixing tub after that time will have to be thrown away, along with the tub.

Too true. And the more that you have mixed, the faster it will go off.

 

[nearthemark]

Any thoughts on the best size screws and hole? The tile that cracked had 4mm screws in a 6mm hole with red rawlplug but was already weakened by a 10cm hole. As that's only the extractor fan I could use smaller screws no problem.

With the radiators, though, where I'd like to use the 4mm screws, is it worth risking the 6mm hole, maybe on grout line? Or would a 7mm hole in the tile, with a 6mm hole into the wall, be better?

Thank you

 

[Keithmac]

I'd have all the Rawl plug completely through the tile and into wall, as long as there is no void behind tile you should be able to tighten screw without cracking tile.

Maybe 6mm hole in wall, 7mm in tile (if you have to) and 5mm screws with red Rawl plugs (in case people lean on radiator).

 

[nearthemark]

I'd have all the Rawl plug completely through the tile and into wall, as long as there is no void behind tile you should be able to tighten screw without cracking tile.

Maybe 6mm hole in wall, 7mm in tile (if you have to) and 5mm screws with red Rawl plugs (in case people lean on radiator).

That seems like a good idea, presumably use the back of a drill bit to tap the rawl plug in. Has anyone here tried the method that Keithmac has suggested?